Plasma hand burner with contact protection

ABSTRACT

A circuit arrangement for plasma hand torches for fusion cutting having a contact protection which comprises a housing, a nozzle disposed in the housing and having an exit opening. A nozzle cap is in electrically conducting connection with the housing. Two conduits ground the housing at two points. A current-feeding source is electrically connected with the two conduits. One of the conduits constitutes a protection conduit and the other of the conduits constitutes an auxiliary conduit. The one of the conduits includes a current relay with first contact and the other of the conduits includes an auxiliary relay and a secondary winding of a low voltage transformer. The auxiliary relay includes a working contact disposed in series with the first contact. The plasma hand torch has an operating relay, and the operating relay is capable of being either switched off or not switched on respectively, by means of said first contact upon occurrence of a short circuit or by the working contact upon interruption of the protection conduit or of the auxiliary conduit.

United States Patent Inventors Appl. No.

Filed Patented Assignee Rudolf Pochert;

, Haase Lothar; Willy Roggenbuch; Peter Wiese, Dresden, Germany- Nov. 4,1968 Jan. 26, 197 l Kjellberg Elecktroden & Maschinen GMBH in VerwaltungFinsterwalde, Germany a corporation of Germany T'LASMA HAND BURNER WITHCONTACT [5 6] References Cited UNITED STATES PATENTS 1,708,072 4/1929Alexander 219/1 3 1X Primary Examiner-Raymond F. HossfeldAttorney-Ernest G. Montague ABSTRACT: A circuit arrangement for plasmahand torches for fusion cutting having a contact protection whichcomprises a housing, a nozzle disposed in the housing and having an exitopening. A nozzle cap is in electrically conducting connection with thehousing. Two conduits ground the housing at two points. Acurrent-feeding source is electrically connected with.

the two conduits. One of the conduits constitutes a protection conduitand the other of the conduits constitutes an auxiliary conduit. The oneof the conduits includes a current relay with first contact and theother of the conduits includes an auxiliary relay and a secondarywinding of a low voltage transformer. The auxiliary relay includes aworking contact disposed in series with the first contact. The plasmahand torch has an operating relay, and the operating relay is capable ofbeing either switched oiT or not switched on respectively, by means ofsaid first contact upon occurrence of a short circuit or by the workingcontact upon interruption of the protection conduit or of the auxiliaryconduit.

PATENTEBJANZSIQII NEW R H L FSkR H ASg WLLY ROGGEN UCK PETER WIESEORNEY.

PLASMA HAND BURNERWITH CONTACT PROTECTION all have the disadvantage ofnot being protected against contacting, so that their use as handtorches is restricted. Even in the known torches which are speciallyconstructed as hand torches, the voltage-carrying nozzle or nozzle capis not protected against accidental contact. Consequently, such plasma 7torches are only suitable forlow operating voltages and conl5 sequentlyare only of low power as for as the plasma jet is concerned.

ln other constructions, the nozzle or nozzle cap is protected fromcontact by a metallic housing which does not carry a voltage. However,there are circumstances under which the housing becomes live, forexample due to insulation breakdown, ionization of the insulating airspace between the nozzle cap and the housing, or passage of the arebetween the nozzle and the housing.

In one of the known arrangements, the nozzle is mounted by v two rubberseals in a nozzle carrier which extends almost as far as the nozzleopening. The rubber seals have the function of sealing the cooling waterchamber, which extends as far as the nozzle, on the one hand relative tothe supplied gas and on the other hand relative to the atmosphere. Forthe electric insulation of the nozzle cap relative to the nozzle or thenozzle carrier, a suitably formed ceramic ring is provided. Thisarrangement has the disadvantage that due to the physical requirements,the nozzle, the nozzle carrier, the nozzle cap and the ceramic ring havea relatively complicated shape.

In addition, the nozzle and the nozzle cap constitute members which aresubject to wear, so that they are required in large numbers. Due tothis, a complicated shape for these members is particularlydisadvantageous.

Moreover, there is the disadvantage that due to the interposition of theceramic ring and the shape of the nozzle and nozzle cap which resultfrom this, as well as the necessary insulation in the region of thenozzle, the hand torch has relative large dimensions. This has thedisadvantage that it can readily obstruct the vision of the operator,and the torch can only be used at low inclination angles relative to thevertical, this being particularly disadvantageous in view of thefrequent necessity for making angular cuts. Finally, it should bementioned that as a result of the large dimension of the torch,

there is a large surface present above the workpiece and the torch isthereby vulnerable to be soiled or damaged by liquid material splashingupwards from the workpiece.

It is one object of the present invention to provide a plasma hand torchwhich avoids the above stated disadvantages.

It is another object of the present invention to provide a plasma handtorchwherein the insulation is arranged between voltage conducting partsand the housing'of the torch in such a manner that while retaining easyexchangeability of the nozzle, and effective cooling of the same, adanger-free operation is enabled.

It is still another object of the present invention to provide a circuitarrangement for a plasma hand torch, wherein a housing of the torch iselectrically connected with a nozzle cap of the torch, is protectivelygrounded at two places through two lines which are connected to thehousing of a current supply unit, a current relay with a nonnally'closedcontact being provided in one of the lines, an auxiliary relay and thesecondary winding of a low-voltage transformer being provided in theother auxiliary line,.the auxiliary relay having a normally open contactwhich is connected in series with the said normally 70 closed contact.An operating relay of the plasma torch is made releasable ornonengageable as a result of opening of the normally closed contact inthe event of a short circuit, or as a result of closure of the normallyopen contact in the event of an interruption in either of the two lines.

Preferably, the nozzle of the torch is connected to the nozzle cap withwith the interposition of an elastic electrically insulating layer. Aprotective ground connection may be made to the housing ofthe plasmatorch.

It is still another object of the present invention to provide a ceramicinsulator at the nozzle end of the torch, disposed concentricallyrelative to the nozzle and the nozzle cap, and extending beyond thenozzle and nozzle cap at the one end. The nozzle, and especially theoutlet opening for the plasma jet, is surrounded by the ceramicinsulator. For the purpose of an easy exchangeability of the nozzle andnozzle cap, the ceramic insulator and the nozzle cap are provided withmutually engaging collars.

In accordance with the present invention, a plasma hand torch isprovided which, while being suitable for a high current density in thecutting jet, can be used without danger even for such workpiecesrequiring a low cutting width and a high cutting speed, suchapplications being not particularly suitable for machine cutting as aresult of the shape and/or the dimensions.

With these and other objects in view, which will become apparent in thefollowing detailed description, the present invention, which is shown byexample only, will be clearly understood in connection withthe.accompanying drawings, in which:

FIG. I is a circuit diagram of the arrangement of the present invention;

FIG. 2 is a fragmentary sectional view of a part of a plasma hand torchaccording to the present invention; and

FIG. 3 is a perspective view of a complete plasma hand torch.

Referring now to the drawings and in particular to FIG. 1, theprotective circuit of a plasma hand torch designed in accordance withthe present invention. is disclosed. A housing 6 of a plasma hand torch,and therewith also the nozzle cap 5, are connected through a protectingline 11 to the protectively grounded housing of a current supply unit12. The protecting line 11 is connected through the winding of a currentrelay 13.

An auxiliary protecting line 14 connected at a second region of thehousing 6 is connected through the winding of an auxiliary relay l5 andthe secondary winding of a low voltage transformer 16, likewise withground.

The normally open contact 17 and the normally closed contact 18 of therespective relays l3 and 15 are connected in series and interlocked withan operating relay 23 of the current supply unit 12, so that theoperating relay 23 is switched off or is prevented from being switchedon, respectively if the protecting line 11 or the auxiliaryline 14 isinterrupted, that is, if the excitation current circuit of the auxiliaryrelay 15 is not closed, so that the auxiliary relay 15 is not excitedand as a result thereof its normally open contact 17 stays open, ashereinafter described.

The connection of the two lines 11 and 14 to different regions of thetorch housing 6 excludes the case that the lines 1] and 14 are onlyconnected to each other but not to the housing 6. The operation of theprotective circuit is as follows:

Upon switching on the main switch (not shown) of the current supply unit12, the operating voltage appears on the ter- 0 minals 20 and 21 and thecontrol voltage on the terminals 24 and 25. The supervising currentcircuit which is fed from the transformer 16 is closed (the supervisingcurrent circuit con sisting of the secondary winding of the transformer,the wind ing of the auxiliary relay 15, the auxiliary line 14, thehousing 6 of the plasma torch, the protective linell, the first winding26 of the current relay l3 and the housing of the current supply unit12), thatis, the housing 6 of the plasma torch is connected with thehousing of the current supply unit 12 and thereby protectively grounded,thus the auxiliary relay l5 responds to the current fed by the actuatedtransformer 16 and closes its working contact 17, the latter beingdisposed in the control circuit comprising the contacts 17 and 18, therelay 23, and a control switch 22.].

By the operation of the control switch 22.1 (i.e. closing the switch22.1 in the control circuit), the operating relay 23 is renderedoperative, and its contact 28 disposed in the torch operating circuitcloses, and the operating voltage appears over the working contact 28 onthe cathode 19. The operating relay 23 switches off in known manner alsothe working gas and the ignition thereof, and thereby the burner isalways in operation.

Ordinarily, housing 6 and nozzle cap 5 are insulated from the highvoltage from terminal 20 by the ceramic insulator 7.

When the control circuit comprising the contacts 18 and 17 isopen-circuitcd (due to either contact 17 or 18 or switch 22.1 beingopen), then the operating relay 23 is inoperative and its contact 28 isopen in the electrode or torch-operating circuit which preventsterminals 20 and 21 from supplying the operating voltage to the torch.

In normal operation, the low-voltage transformer 16 is initiallyactuated upon closing the main switch (not shown), which places thecontrol voltage on terminals 24 and 25, thereby causing relay to closeits normally open contact 17 in the control circuit. Switch 22 (FIG. 3)is then actuated to close contact 22.1 which now closes the controlcircuit and thereby and causes the operating relay 23 to be actuated bythe voltage at terminals 24 and 25, thereby closing contact 28 in thetorch operating circuit and permitting the high voltage on terminals and21 to provide a high voltage across the electrode 19 and workpiece,causing the torch to be in operation. Since the housing 6 is insulatedfrom the high voltage during normal operating, relay 13 in line 11receives no actuating current (the current from the low-voltagetransformer 16 being insufficient to open contact 18 in the controlcircuit, and this contact 18 remains closed and the torch may beoperated continuously.)

However, at the instant of an insulation break, etc., and a jumping ofthe are (for instance, as a result of a defective ceramic insulator 7)from the cathode 19 over the nozzle 1 to the nozzle cap 5, the operatingvoltage which appears at the terminals 20 and 21 causes the housing 6 tomomentarily have a high voltage and sends a high actuating currentthrough the protective line 11, and the winding 26 of the current relay13. This immediately actuates the currentrelay l3 sufficiently to causecontact 18 in the control circuit to open, thereby opening or breakingthe control circuit in which the operating relay 23 is disposed andthereby switching off the latter and causing the operating relay 23 toopen its contact 28 in the control circuit and prevent terminals 20 and21 from supplying the high voltage to the electrode 19 and thus to thedefective insulator and torch housing 6. The opening of contact 18 inthe relay 23 circuit i.e., the control circuit, however, is designedsuch that the contact 18 closes a self-holding or self-locking circuitin which is disposed the second winding 27 of the current relay 13,i.e., the second winding 27 of the current relay 13 now becomes actuatedby the voltage across terminals 24 and 25, in this self-locking circuit,thus maintaining the contact 18 open in the control circuit of theoperating relay 23, but held closed in the self-locking circuit, so thateven though the high operating voltage to the electrode 19, and thus towinding 26 of the current relay 13 in the insulationdamaged condition ismomentarilyremoved, the contact 18 is assured of not retuming to againactuate the operating relay 23, before the main switch is turned 011' toremove the voltages across the terminals 20 and 21 as well as terminals24 and 25.

The-nozzle 1, the defective insulator, the nozzle cap 5, the protectiveline 11 and the winding 26 of the current relay 13 only momentarilyconduct the high current and consequently are protected beforedestruction.

lf without the self-holding feature of the current relay 13 over thecontact 18 and the second winding 27, the response of the current relay13 otherwise would thereafter cause the operating voltage of the cathode19 to be switched off, but the current relay 13 would again fall off andclose its contact 18 and with the still-actuated control switch 22.1,the operating relay 28 would repeat to switch the operating voltage onagain the to the cathode 19 and hence through the defective insulation.This is avoided by the self-maintaining operation of the relay 13 by thesecond winding 27 in the self-locking circuit of the relay 13.

After the switching out of the main switch of the current supply unit12, the current relay 13 falls off and the contact 18 closes again inthe control circuit and the switching arrangement is again in thecontrol circuit and the switching arrangement is again operatively readyafter removal of the cause of damageand switching on of the main switch.

The switching out in accordance with the working results by means ofrelease of the actuating element 22 of the control switch 22.1, wherebythe latter is opened and the operating relay 23 falls off.

If the supervising current circuit, i.e., lines 11 and 14 isinterrupted, at some point, for instance, in the path of the protectingline 11, by which the protection device is no longer assured throughfaults of the protective ground of the housing 6 ,of the plasma torch,thus the auxiliary relay 15 does not respond and falls away,respectively, when such interruption during the working occurs. Therebythe working contact 17 of the auxiliary relay 15 opens in the controlcircuit and the operating relay 23 no longer responds (the actuatedcontrol switch 22.1 still being actuated), and falls off, respectively,whereby again the operating voltage to the electrode 19 of the plasmatorch is switched off.

By this em exemplified interruption of the protective line 11 thesecondary voltage of the transformer 16 appears over the winding of theauxiliary relay 15 and the auxiliary line 14 at the housing 6 of theplasnia torch. Therefore this voltage is a harmless auxiliary voltage.The transformer 16 serves moreover for the disconnecting of theground-connected supervising current circuit of the remaining controlcurrent circult.

On the other hand, during normal operation, if the low-voltagetransformer 16 is turned off, the auxiliary relay 15 is shut off andcontact 17 opens its contact 28 in the control circuit, thereby turningoff the operating relay 23 and also cutting off the operating voltage tothe electrode 19. The transformer 16 may be used as a safety devicepreventing the turning on of the torch, even by switch 22, unlesstransformer 16 is operating.

The operation of transformer 16 which is sufficient to actuate theauxiliary relay 15 to close its contact 17 is insufficient to cause thecurrent relay [3 to open its contact 18, since it is a low-voltagetransformer, the relay 13 requiring a higher current through the winding26 in order to open its contact 18.

That is, in the event of a possible establishment of the are from thecathode 19 over the nozzle 1 to the nozzle cap 5, the operating voltagewhich is applied to the terminals 20 and 21 causes a high current toflow through the protecting line 11. This causes the current relay 13 torespond so as to open its normally closed contact 18, which results inthe operating relay 23 interrupting the operating voltage, whereupon thenozzle 1, the nozzle cap 5 and the protecting line 11 are isolated fromthe voltage. In this manner these parts carry the high current for onlya short period of time, and they are thus protected from damage.

Referring now again to the drawings and more particularly to FIG. 2, theplasma hand torch is disclosed in detail, and comprises a nozzle 1,preferably of copper, which is centralized in the nozzle carrier 2 andsealed at its rear face by a rubber seal 3. By means of an elasticvoltage-resistant seal 4, the nozzle 1 is electrically insulated formthe nozzle cap 5. The nozzle cap 5 is connected by means of screwthreads with the protectively grounded housing 6.

By means of a ceramic insulator 7, against which the nozzle cap 5engages, the seal 4 is pressed against the nozzle 1 and thus seals acooling water chamber 8. The nozzle 1 is accordingly directly watercooled, and is nevertheless readily exchangeable by screwing off thenozzle cap 5.

An insulator 9 insulates the nozzle carrier 2 relative to the housing 6of the plasma hand torch and contains channels 10 for the supply andreturn of the cooling water. The ceramic insulator 7, in addition toserving for thermally protecting the seal 4, serves for elongating theelectrical leakage path and as a contact protection of the nozzle 1.

Referring now again to the drawings and more particularly to FIG. 3, anactuating element 22 of the control switch for the operating relay ismounted in the handgrip of the torch. This actuating element 22, whenmade of metal, should be included in the protective circuit. Theoperating relay switches the operating voltage and also the operatinggas and the ignition. The remaining operation takes place automatically.

While we have disclosed one embodiment of the present invention, it isto be understood that this embodiment is given by example only and notin a limiting sense.

We claim:

l. A circuit arrangement for plasma hand torches for fusion cuttinghaving a contact protection, comprising:

a housing;

a nozzle disposed in said housing and having an exit opening;

a nozzle cap in electrically conducting connection with said housing;

two conduits grounding said housing at two points;

a current supply unit operatively electrically connected with said twoconduits;

one of said conduits constituting a protection conduit and the other ofsaid conduits constituting an auxiliary conduit;

said one of said conduits including a current relay with a firstcontact;

said other of said conduits including an auxiliary relay and a secondarywinding of a low-voltage transformer;

said auxiliary relay including a working contact disposed in series withsaid first contact;

said plasma hand torch having an operating relay; and

said operating relay capable of being rendered to switch off or not toswitch on respectively, by means of said first contact upon occurrenceof a short circuit or by said working contact upon breaking of saidprotection conduit or of said auxiliary conduit.

2. The circuit arrangement, as set forth in claim 1, which includes anelastic, electrically insulating sealing connecting said nozzle withsaid nozzle cap.

' 3. The circuit arrangement, as set forth in claim 1, which includes aceramic insulation disposed concentrically about said nozzle and saidnozzle cap, and projecting beyond said nozzle cap simultaneouslyenclosing said exit opening of said nozzle.

4. The circuit arrangement, as set forth in claim 3, which includes acollar each for said ceramic insulation, as well as for said nozzle cap.

5. An arrangement for a plasma hand torch including a torch housingelectrically connected to a nozzle cap of the torch, comprising:

a current supply unit including a protective housing;

a protecting line connected to said torch housing at a first positionand grounded to said protective housing;

an auxiliary line connected to said torch housing at a second positionand grounded to said protective housing;

a control circuit;

a current relay disposed in said protecting line and including anormally closed contact disposed in said control circuit;

an auxiliary relay disposed in said auxiliary line and including anormally open contact connected in said control circuit in series withsaid normally closed contact;

a low-voltage transformer including a secondary winding,

the latter disposed in said auxiliary line;

an operating circuit means for providing an operating voltage to saidplasma torch;

means for insulating said torch housing and nozzle cap from saidoperating voltage during normal conditions; and

an operating relay means for said plasma torch operatively connected insaid control circuit and having a closable contact disposed in saidoperating circuit means for preventing a letter latter from providing anoperating voltage to said plasma torch upon open circuiting of saidcontrol circuit.

6. The arrangement, as set forth in claim 5, wherein: said currentsupply unit selectively provides high voltage to said operating circuitmeans and to said low-voltage transformer:

said low-voltage transformer designed to supply sufficient current tosaid auxiliary relay when said transformer is ac tuated by said currentsupply unit so as to close said normally open contact in said controlcircuit;

said auxiliary line an said protective line constituting a supervisorycircuit so said low-voltage transformer designed to supply insufficientcurrent to said current relay when said transformer is actuated by saidcurrent supply unit so as to maintain said normally closed contact inits closed condition is in said control circuit;

an operating switch for said control circuit; and

said current relay including a separate winding connected to saidcurrent supply unit and said normally closed contact movably disposed soas to close the circuit between said separate winding and said currentsupply unit when a high current passes through said current relay andsaid normally closed contact open circuits said control circuit.

1. A circuit arrangement for plasma hand torches for fusion cuttinghaving a contact protection, comprising: a housing; a nozzle disposed insaid housing and having an exit opening; a nozzle cap in electricallyconducting connection with said housing; two conduits grounding saidhousing at two points; a current supply unit operatively electricallyconnected with said two conduits; one of said conduits constituting aprotection conduit and the other of said conduits constituting anauxiliary conduit; said one of said conduits including a current relaywith a first contact; said other of said conduits including an auxiliaryrelay and a secondary winding of a low-voltage transformer; saidauxiliary relay including a working contact disposed in series with saidfirst contact; said plasma hand torch having an operating relay; andsaid operating relay capable of being rendered to switch off or not toswitch on respectively, by means of said first contact upon occurrenceof a short circuit or by said working contact upon breaking of saidprotection conduit or of said auxiliary conduit.
 2. The circuitarrangement, as set forth in claim 1, which includes an elastic,electrically insulating sealing connecting said nozzle with said nozzlecap.
 3. The circuit arrangement, as set forth in claim 1, which includesa ceramic insulation disposed concentrically about said nozzle and saidnozzle cap, and projecting beyond said nozzle cap simultaneouslyenclosing said exit opening of said nozzle.
 4. The circuit arrangement,as set forth in claim 3, which includes a collar each for said ceramicinsulation, as well as for said nozzle cap.
 5. An arrangement for aplasma hand torch including a torch housing electrically connected to anozzle cap of the torch, comprising: a current supply unit including aprotective housing; a protecting line connected to said torch housing ata first position and grounded to said protective housing; an auxiliaryline connected to said torch housing at a second position and groundedto said protective housing; a control circuit; a current relay disposedin said protecting line and including a normally closed contact disposedin said control circuit; an auxiliary relay disposed in said auxiliaryline and including a normally open contact connected in said controlcircuit in series with said normally closed contact; a low-voltagetransformer including a secondary winding, the latter disposed in saidauxiliary line; an operating circuit means for providing an operatingvoltage to said plasma torch; means for insulating said torch housingand nozzle cap from said operating voltage during normal conditions; andan operating relay means for said plasma torch operatively connected insaid control circuit and having a closable contact disposed in saidoperating circuit means for preventing a letter latter from providing anoperating voltage to said plasma torch upon open circuiting of saidcontrol circuit.
 6. The arrangement, as set forth in claim 5, wherein:said current supply unit selectively provides high voltage to saidoperating circuit means and to said low-voltage transformer: saidlow-voltage transformer designed to supply sufficient current to saidauxiliary relay when said transformer is actuated by said current supplyunit so as to close said normally open contact in said control circuit;said auxiliary line an said protective line constituting a supervisorycircuit so said low-voltage transformer designed to supply insufficientcurrent to said current relay when said transformer is actuated by saidcurrent supply unit so as to maintain said normally closed contact inits closed condition is in said control circuit; an operating switch forsaid control circuit; and said current relay including a separatewinding connected to said current supply unit and said normally closedcontact movably disposed so as to close the circuit between saidseparate winding and said current supply unit when a high current passesthrough said current relay and said normally closed contact opencircuits said control circuit.